The cost of energy has continued to steadily rise as power utilities try to cope with continually growing demands, increasing fuel prices, and stricter regulatory mandates. Power utilities must maintain existing power generation and distribution infrastructure, while simultaneously finding ways to add more capacity to meet future needs, both of which add to costs. Burgeoning energy consumption continues to impact the environment and deplete natural resources.
A major portion of rising energy costs is borne by consumers, who, despite the need, lack the tools and wherewithal to identify the most cost effective ways to appreciably lower their energy consumption. For instance, no-cost behavioral changes, such as adjusting thermostat settings and turning off unused appliances, and low-cost physical improvements, such as switching to energy-efficient light bulbs, may be insufficient. Moreover, as space heating and air conditioning together consume the most energy in the average home, appreciable decreases in energy consumption can usually only be achieved by making costly upgrades to a building's heating or cooling envelope or “shell.” However, identifying those improvements that will yield an acceptable return on investment in terms of costs versus energy savings requires first determining building-specific parameters, including thermal conductivity (UATotal) and infiltration.
Heating, ventilating, and air conditioning (HVAC) energy costs are directly tied to a building's thermal conductivity. A poorly insulated home or a leaky building will require more HVAC usage to maintain a desired interior temperature than would a comparably-sized but well-insulated and sealed structure. Reducing HVAC energy costs, though, is not as simple as merely choosing a thermostat setting that causes an HVAC system to run for less time or less often. Rather, numerous factors, including thermal conductivity, HVAC system efficiency, heating or cooling season durations, and indoor and outdoor temperature differentials all weigh into energy consumption and need be taken into account when seeking an effective yet cost efficient HVAC energy solution.
Conventionally, an on-site energy audit is performed to determine a building's thermal conductivity UATotal. An energy audit is a labor intensive and intrusive process that involves measuring a building's physical dimensions; approximating insulation R-values; detecting air leakage; and estimating infiltration through a blower door test. A numerical model is run against the audit findings to solve for thermal conductivity. The UATotal is combined with heating and cooling season durations and adjusted for HVAC system efficiency, plus any solar or non-utility supplied power savings fraction. An audit report is then presented as a checklist of steps that may be taken to improve the building's shell.
The blower door test part of the audit presents several challenges. Before the test, monitoring equipment must be calibrated on-site to building-specific factors and airtight covers must be placed over all HVAC vents. Exterior doors, windows and other openings must also be sealed and a blower door panel will be temporarily placed into an outside doorway. During the test, a fan in the blower door panel forces air into or pulls air out of the building to respectively generate a positive or negative pressure differential to the outdoors, and pressure differences are measured. Following completion, test results are converted into pressure values representing normal conditions from which infiltration is then estimated.
As an involved process, a blower door test can be costly, time-consuming, and invasive for building owners and occupants. Throughout the test, trained personnel must be on-site. As well, the building is rendered temporarily uninhabitable and must remain closed up for an extended period of time while a noisy blower fan is run. In addition, a blower door test requires specialized equipment and trained personnel, which adds to the cost. Notwithstanding, blower door test results are fallible and are simply estimates. Calibration errors that can invalidate a test can and do occur; moreover, testing results need to be translated from high pressure testing conditions to normative building operating conditions with reliance on an approximation that projects infiltration losses.
Therefore, a need remains for a practical model for determining actual and potential energy consumption for the heating and cooling of a building.
A further need remains for an approach to estimating structural infiltration without the costs and inconvenience of blower door testing methodologies.